It’s not like this is a surprise, points out BusinessWeek — the USPS has been warning the government that it didn’t have the means to pay the $5.5 billion payment, which was due last September, or another one for $5.6 billion by Sept. 30 this year. The payments are required and go toward future retirees’ health care. The USPS says those payments are causing it to be financially unstable and that it needs help from Congress.

So what’s the hold-up in Congress? Legislation passed by the Senate in April that would return $10.9 billion that was overpaid into health-fund benefit accounts for those retirees who have yet to retire might help, but the House has yet to act on a different bit of legislation. And if it hasn’t yet, it’s doubtful it will by tomorrow.

The USPS has more employees than any other U.S.-based public company other than Walmart, and lost $3.2 billion in the first quarter of 2012. It’s going to run out of cash in October unless that required payment toward health care, which went into effect in 2006, goes away as well as big services changes like the end of Saturday mail delivery.

A statement on the USPS site reads:

“The Postal Service continues to implement its strategic plan. However, comprehensive postal legislation is needed to return the Postal Service to long-term financial stability. We remain hopeful that such legislation can be enacted during the current Congress.”

Included in the strategic plan would be a cut of around 220,000 jobs and the closing of various mail-processing plants to cut down on costs. The USPS was going to totally shut down some of its post offices in an earlier plan to avoid default, until opposition in Congress put a stop tot hat plan. Instead, it’ll cut operating hours at many locations in a bid to save $500 million per year.

Proponents of the plan to stop paying into the retiree fund say there’s plenty of cash to go around for decades to come — $45 billion.

If we thought our retired members were in danger of losing their health care, we’d be screaming bloody murder about it,” said the president of the National Association of Letter Carriers union in a statement.